Jodi - My MCHN told me that some babies pretty much skip the rolling milestone and just do the sitting up/crawling instead. Xander usually just lets his head flop down during tummy time as he super slack. He also just lets his head flop if you pull him by his arms to a sit from lying down; yet he holds his head just fine when I sit him up so obviously the neck muscles are getting stronger... the way I see it is that at least when I make him sit upright, he is working these muscles and making them stronger. I have been told by health nurse that carrying him 'aeroplane' style has the same effect on the neck as tummy time.